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Last update: 5 Dec 2008
An individual-based Dynamic Global Vegetation Model SEIB-DGVM has been adapted to tropical rain forest in Malaysia by incorporating formulations and parameters of an individual-based gap dynamics model FORMIX3. After tuning, the model appropriately reconstructed forest structure (i.e., size structure, LAI, and woody biomass) and carbon fluxes (i.e., GPP and NPP) of a dipterocarp forest in Pasoh, Peninsular-Malaysia. Sensibility test shows the model is robust; forest structure and ecosystem function are moderately fluctuated by changes in tuning parameters and climatic environments. Sensibility test also shows prosperity and decay of dominant species group, which monopolize canopy layer, have large impacts on those of less abundant species groups. This result indicates that environmental changes may give considerable impacts on biodiversity of subdominant species, even if it did not give apparent impacts on dominant canopy species and whole forest structure. In simulations without the gap formation formulation, woody biomass was overestimated, and a shade intolerant PFT was eliminated. This indicates that taking gap formation into consideration is essential for appropriately simulating forest biomass and biodiversity using an individual based model.
Several pieces of evidence show that the recently developed Optimal Uptake kinetics is a superior way to describe the uptake of nutrients (and, thereby the growth) of phytoplankton and bacteria. Mostly, I will present a recent analysis of values of the half-saturation constant for nitrate uptake determined during oceanic cruises. I will also briefly review evidence from modeling studies of 1. experiments that measured steady state nutrient uptake by phytoplankton, 2. an iron-enrichment experiment, and 3. steady state experiments that measured bacterial growth.
Half-saturation "constants" are not the way to describe nutrient uptake: Phytoplankton supply the base of the marine food web and drive the biogeochemical cycles of carbon and nutrients. Over much of the ocean their growth is limited by their uptake of nitrogen (as nitrate), which has most commonly been described by the hyperbolic Michaelis-Menten (MM) equation, but lack of a theory to explain variations in MM constants has hindered our ability to predict the response of marine ecosystems to changes in environmental conditions. The MM equation fits data from short-term experiments well, but does not agree with steady-state experiments over wide ranges of nutrient concentrations. The recently developed Optimal Uptake kinetics does agree with the latter and can also describe the observed pattern of MM half-saturation constants from field experiments. We present a simple explanation for the observed pattern of nitrate uptake in terms of Optimal Uptake kinetics, which provides a basis for predicting effects of climate change on marine ecosystems and biogeochemical cycles.
The realistic modeling of the radiative transfer within a canopy is important issue for both retrieval of the terrestrial ecosystem information from satellite spectral reflectance data and evaluation of the canopy photosynthesis. Three dimensional modeling is required for spatially heterogeneous vegetation like forest.
We have been developing and improving the 3-D radiative transfer model, FLiES. In this seminar, we will review the canopy RT model including current status, inter-comparison activity named RAMI (RAdiation Model Intercomparison) initiated by the Joint Research Center, EU. Then I will introduce some application results from the model and future plan of the model improvement and application.
I would like to introduce our recent results including members in Hokkaido University and Tohoku-Suiken, especially, future projection of Japanese sardine by Okunishi-san. I would also like to introduce global COE program in Hokkaido University.
Historically, northern peatlands have functioned as a carbon sink by sequestering a large amount of soil organic carbon (SOC) mainly due to low decomposition rates in cold, largely waterlogged soils. Water table, an essential determinant of SOC dynamics, interacts and coevolves with peat SOC; due to the high water holding capacity and the low hydraulic conductivity of peat, accumulation of SOC results in a higher water table that further lowers SOC decomposition rates (positive feedback). Although this 2-way interaction between hydrology and biogeochemistry has been noticed in several observational and analytical studies, the complex behavior of peat dynamics was not reproduced in process-based simulation of soil hydrology and biogeochemistry. By continuously updating peat depths in a coupled soil physical-biogeochemical model, we found that the feedback between water table and peat depth increases temperature sensitivity of peat decomposition and intensifies SOC loss under climate change. Our model successfully reproduces both fast-timescale dynamics of water table and soil temperature and long-term SOC equilibria of shallow and deep peatlands in northern Manitoba, Canada. In long-term simulation, an experimental warming of 4 °C caused 40 % SOC loss from the shallow peat, and 86 % from the deep peat. Peatlands will quickly respond to the expected warming in this century by losing labile SOC in dry periods.
In order to clarify the impact of global warming on marine ecosystems, we developed a 3-D high-resolution ecosystem model with off-line calculation method which can directly use predicted results of climate models as a physical field of the ecosystem model. Our model, COCO-NEMURO which has a horizontal resolution of 1/4 by 1/6 degrees, consists of PICES NEMURO (North Pacific Ecosystem Model for Understanding Regional Oceanography) coupled with COCO (CCSR Ocean Component Model). We applied this model into the western North Pacific, and conducted a global warming experiment using predicted physical fields by a high-resolution climate model (the CCSR/NIES/FRCGC climate model which contributed to the IPCC-AR4). The experiment was conducted with an idealized scenario in which an atmospheric CO2 concentration increases by 1% per year. Under the global warming condition, our model projected a significant decrease in the maximum phytoplankton biomass by 25 % during the spring bloom in the subarctic-subtropical transition region. This result supports the projection of Hashioka and Yamanaka (2007) with a medium resolution version of COCO-NEMURO (1 by 1 degrees). However, it is interesting that the predicted maximum biomass in spring in the subarctic region increases by 20 % in the new experiment with high-resolution model, while decrease in the annually averaged biomass. These results suggest that the impact of global warming would significantly appear in the specific season and regions. We show the reason of these changes based on changes in the environmental factors associated with global warming (e.g., temperature, nutrient and light conditions).
The Kuroshio Extension (KE) is the highest level of eddy variability in the North Pacific. Frontal disturbance of the KE cause mesoscale eddies which contribute to accelerating local biological production. Effects of mesoscale eddies on marine ecosystem in the KE is investigated using a simplified four-component ecosystem (NPZD) model embedded in an eddy-resolving ocean general circulation model (OFES).
The model reproduces the interannual variability of sea surface height anomaly (SSHA) in the KE along zonal band of 32-34N from 2002 to 2006, and distribution of high surface chlorophyll corresponds to low SSHA (Figure 1). The westward propagating cyclonic eddies lift nutrient-rich thermocline into the euphotic zone and maintain the high productivity in the subsurface layer before mixed layer development. In fall, some of cyclonic eddies are combined with another cyclonic eddy from subarctic region (high nutrient water) and the biological productivity in the subsurface layer is high. Vertical velocity also plays an important role of nutrient supplying near the KE meander.
Solar radiation is the fundamental driver of ecosystem functioning and an essential factor in process models of the terrestrial carbon cycle. However, in the past this role has received less attention relative to other key problems in carbon cycle studies and vegetation-climate relations. This presentation reviews recent research at FRCGC-ECRP that contributes toward filling this gap. Topics include observational studies of photosynthetically active radiation (PAR) in the Southeast Asia region, and development of new, innovative instruments that enhance current capabilities for PAR measurement and monitoring. Results from this research contribute toward improved knowledge and understanding of PAR and its role as a determinant of photosynthesis and ecosystem-atmosphere CO2 exchange in the terrestrial biosphere.
During the last 3 years, a process-based terrestrial ecosystem model was developed to capture exchange of various trace gases. In this seminar, I show recent results concerning the global simulation to evaluate the net budget of Global Warming Potential (GWP) over terrestrial ecosystems. Net budget of major greenhouse gases, i.e. carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) was included on the basis of specific biogeochemical mechanisms: for example, CH4 oxidation by Ridgwell’s scheme, CH4 emission by Cao’s, and N2O emission by Parton’s scheme.
Global simulation was conducted from 1901 to 2100, using historical climate data by CRU TS2.1 and future AOGCM projection driven by prescribed atmospheric composition, at spatial resolution of 0.5-deg x 0.5-deg. Based on net CO2, CH4, and N2O budget for each grid, net GWP of terrestrial ecosystems was estimated. It was shown that, in 2000, terrestrial biosphere would be a net CO2 sink by 2.2 Pg C per year as a difference between photosynthesis and respiration, but largely offset by ancillary emissions from land-use change and biomass burning. Remarkably, net emissions of CH4 and N2O with higher radiative forcing had a comparable effect on the total GWP with substantial heterogeneity. Additionally, plant CH4 emission under aerobic condition (recently found by Keppler et al.) was estimated as 87.6-130.5 Tg CH4 per year, implying higher GHG source to the atmosphere. These results were compared with previous individual studies.
In previous seminars, site-scale validation at Takayama and Fujiyoshida forests was reported. Now, I started to apply VISIT to a paddy field site in Japan to examine and improve CH4 emission scheme; possibly, some preliminary results will be shown.
Analyzing the historical collections of zooplankton in details, previous studies have revealed phenology and biogeographical shift of zooplankton species in the both side of North Pacific after the 1970s, and influences of coastal current dynamics induced by the Aleutian Low dynamics and/or recent warming trend were suggested. However, the regionally specific processes linking climate to zooplankton variation was less clear partly because no detailed data were available for phytoplankton time-series in contrast to the zooplankton data. Nitrogen stable isotope ratio of zooplankton indicates their feeding habit, and thus the phytoplankton abundance, and can be a useful clue to understand the bottom-up control of the lower trophic level productivity. In this study, we investigated regional differences in ecosystem responses to the common climatic forcing in the North Pacific based on delta-nitrogen 15 of Neocalanus species, which were widely distributed and dominant in the subarctic NP. Time-series delta-nitrogen 15 of Neocalanus cristatus, N. plumchrus, and N. flemingeri collected in the western, central and eastern NP were compared. Average delta-nitrogen 15 of the plankton varied among the regions according to its base concentration. Within each region, interannual variation of delta-nitrogen 15 was similar among the three species, indicating the common bottom-up control. However, the variation was not similar among the regions. Causes of the regionally specific changes in the delta-nitrogen 15 will be discussed for each region.
For the better understanding of the carbon cycle in the global ecosystem, investigations on the spatio-temporal variation of the carbon stock which is stored as vegetation biomass is important. The sensor "PALSAR (Phased Array type L-band Synthetic Aperture Radar)" of the satellite "ALOS (Advanced Land Observing Satellite)", launched in January 2006, provides the information which can be used for the above-ground biomass estimation.
To derive the biomass from satellite measurement, it is inevitable to acquire in situ biomass by ground-based survey. Moreover, such ground-based information has to be acquired at as possible many sites for developing a reliable estimation algorithm, so a quick measurement method is required. We applied a way that is a combination of Bitterlich Angle Count Sampling method and Sampled-tree Measuring method (BACS-STM) as a quick method. First, a tree which has wider trunk than a threshold viewing angle is identified by the relascope from a representative point in the target forest. Next, the biomass of the tree is estimate by the allometric equation with the tree height and diameter measurements. Through these processes, the biomass per unit area in the forest is estimated.
In July 2007, a forest survey was carried out in the south-north transect (about 300km long) along the Trans-Alaska Pipeline which profiles the ecotone from boreal forest to tundra in Alaska. Since several papers reported that the recent secular change is apparent in the ecotone in Alaska, this transect would be appropriate for the long term biomass monitoring. 29 forests along the transect were targeted for the survey, and their biomasses were measured. Consequently, it was revealed that the forest biomass distribute from 5 to 100 ton/ha (dried matter). BACS-STM took only about 30 minutes for measuring the forest biomass at one point, and was demonstrated that the method was very suitable for the acquisition of the ground truth biomass for the estimation by the satellite measurement.
The North Pacific is well known as one of the most biologically productivity regions in the world ocean. High primary productivity and strong air-sea interactions characterize the carbon cycle of this region. Understanding the role of biological pump in the ocean and monitoring variability of the chlorophyll a (chl-a) and primary productivity is very important to clarify the geochemical cycles. Ocean color remote sensing is a useful new tool for continuously monitoring the temporal and spatial variability of chl-a concentration, and now over 10-year ocean color remotely sensed data sets have provided. In this study, we will describe seasonal and inter-annual variability of chl-a concentrations and examine recent trends in chl-a variability focused on the North Pacific using ocean color sensor (SeaWiFS) during 1997-2007. To clarify the factors controlling phytoplankton variability, we utilized a combination of satellite remote sensing data from AVHRR (Sea Surface Temperature), SeaWiFS (PAR: Photosynthetically Active Radiation, SSM/I (wind speed), as well as climatology data. Finally we will discuss the distribution patterns of chl-aand their controlling factor in the North Pacific in relation to climatic forcing such as ENSO and/or monsoonal wind.
It was recognized that atmopsheric CO2 growth rate is closely correlated with large-scale climatic events, i.e. teleconnections such as El Nino and Souther Oscillation (ENSO). In this seminar, I will show recent results on the correlation between teleconnection indices and terrestrial carbon budget estimated with a process-based ecosystem model (VISIT). I found that, besides ENSO, the Indian-Ocean Dipole Mode and Arctic Oscillation would exert considerable effects on global terrestrial CO2 budget. Also, I will make a discussion using several observational data.
Phytoplankton supply the base of the marine food web and drive the biogeochemical cycles of carbon and nutrients. Over much of the ocean their growth is limited by their uptake of nitrogen (as nitrate), which has most commonly been described by the hyperbolic Michaelis-Menten (MM) equation, but lack of a theory to explain variations in MM constants has hindered our ability to predict the response of marine ecosystems.
This equation fits data from short-term experiments well, albeit with different constants under different conditions, but does not agree with steady-state experiments over wide ranges of nutrient concentrations. The recently developed Optimal Uptake kinetics, which does agree with the latter, can also describe the observed pattern of MM half-saturation constants from field experiments. This simple explanation for the observed pattern of nitrate uptake provides a basis for predicting the effects of climate change on marine ecosystems and biogeochemical cycles.
Chlorofluorocarbon (CFC) and hydrography are used to investigate the capability of numerical model in simulation of water mass and tracer distributions in the northwestern Indian Ocean (Arabian Sea), where low oxygen minimum water in the subthermocline depths is one of the characteristic features. The observed CFC at a meridional section across the central Arabian Sea exhibits two deep penetration structures: one is on the equator and another is near the northern boundary. The model simulates the equatorial deep penetration which is related with eastward advection on the equator; however, the modeled penetration north of the equator is limited in surface layer. This feature is consistent with the model-data difference in salinity, which exhibits long-term trend into lower values in the model. These results seem to be induced by too low water exchanges with the other oceans especially the marginal seas. A preliminary study by using an idealized tracer advection model will be presented to study the source and pathways of waters in the Arabian Sea.
Grassland is one of the most widespread vegetation types in Asian mid-latitude. In this seminar, I show some preliminary results of high resolution mapping of the grassland biomass using Terra/ASTER imagery. Also, decadal (1998-2006) scale changes in the grassland biomass were detected using SPOT/VEGETATION and Terra/MODIS satellite.
In situ measurements of total and diffuse photosynthetically active radiation (PAR, 400-700 nm) were combined with modeling to investigate the effects of atmospheric scattering by clouds on the surface PAR regime, forest canopy PAR absorption, and photosynthetic rates for a moist tropical site at Putussibau, West Kalimantan Province, Indonesia (0.84N, 112.93E). Time-series PAR data collected in 2007 are characterized by large diffuse PAR fractions and frequent occurrence of enhanced global PAR irradiance (often exceeding the extraterrestrial flux) associated with reflectance and scattering by broken cloud fields. Simulations of canopy-absorbed PAR and gross photosynthesis with the Forest Light Environmental Simulator (FLiES) demonstrate the potential role of clouds in controlling forest canopy light-use efficiency and rates of photosynthesis and vegetation-atmosphere carbon exchange in this moist tropical environment. Recent progress in establishing a unique PAR sensor network in SE Asia and related research activities and plans will also be reported.
What will happen on the stock of commercial fishes in the Northern Pacific by global warming? We will forecast the future status of fish stock based on the outputs from global atmosphere - ocean - terrestrial coupled model of A3 scenario. Hokkaido stock of chum salmon will disappear by 2100 although chum salmon in Bering Sea can still keep the stock. Honshu stock of walleye pollack will collapse in 2050 and Hokkaido stock will decrease dramatically in 2100. The spawning season of Japanese common squid will move one-two months forehead than the present season. NEMURO and NEMURO.FISH was developed by PICES MODEL TT, Hashioka et al. (2007) predicted the change of lowetrophic biomasses in global warming case. Bio-energetic model of common squid in Japan Sea showed the difference of growth as well as the possible change of its migration route. We will discuss the future possibility of NEMURO applications on the forecast of ecological state.
The spatial and temporal dynamics of tropical forest functioning are poorly understood, partly attributed to a weak seasonality and high tree species diversity at the landscape scale. Recent neotropical rainforest studies with local tower flux measurements have revealed strong seasonal carbon fluxes that follow the availability of sunlight in intact forests, while in areas of forest disturbance, carbon fluxes moreclosely tracked seasonal water availability. These studies showed a strong seasonal correspondence of satellite measures of greenness (vegetation indices) with ecosystem carbon fluxes in both intact and disturbed forests, that suggest the potential for larger scale extension of tower flux measurements with satellite data.
We investigated the seasonal patterns and relationships of local site tower flux measures of gross primary productivity (Pg) with independent MODIS satellite measures across three Monsoon Asia tropical forest types, encompassing drought-deciduous, dry evergreen, and humid evergreen secondary tropical forests. In contrast to neotropical forests, the tropical forests of Monsoon Asia are more extensively degraded and heterogeneous due to intense land use pressures, and therefore may exhibit unique seasonal patterns of ecosystem fluxes that are more likely water limited and drought-susceptible.
Our results show significant phenologic variability and response to moisture and light controls across the three tropical forest sites and at the regional scale. The drier tropical forests were primarily water-limited, while the wet evergreen secondary forest showed a slight positive trend with light availability. Satellite greenness observations were generally synchronized and linearly related with seasonal and interannual tower flux Pg measurements at the multiple sites and provided better opportunities for tower extension of carbon fluxes than other satellite products, such as the MODIS Pg product. Satellite enhanced vegetation index (EVI)-derived Pg images revealed strong seasonal variations in photosynthetic activity throughout the Monsoon Asia tropical region.
We have investigated the effects of meso-scale eddies on the global CFC-11 inventory distribution by comparing two different spatial resolution models. The CFC-11 simulation is carried out by coarse resolution (0.5 x 0.5) and eddy-resolving (0.1 x 0.1) models. In the Southern Ocean, the eddy-resolving model is a good performance for the CFC-11 inventory distribution compared with the coarse resolution model, especially between 60S and 30S. The eddy-resolving model explicitly simulate meso-scale eddies and improves the structure of upper ocean stratification in the Southern Ocean. The difference of zonal integrated CFC-11 inventory between the eddy-resolving model and observed is -11% between 60S and 30S. The coarse resolution model underestimates the CFC-11 inventory by 27%. The statistical analysis for the zonal integrated CFC-11 inventory between the model and observed provides that the eddy-resolving model has a good skill for the reproduction of CFC-11 inventory distribution.